(1) Filed of the Invention
The invention relates to a heating/cooling circuit for a motor vehicle according to the preamble of claim 1, an air-conditioning system containing said heating/cooling circuit and a method for controlling the air-conditioning system.
(2) Description of Related Art
JP-A-4-278153 discloses a heating/cooling circuit for an air-conditioning system with a deicing mode, deicing being carried out by increasing the degree of opening of an expansion valve and by reducing the quantity of air supplied to an interior heat exchanger. In this case, since the degree of opening of the expansion valve is increased, both the interior heat exchanger and the exterior heat exchanger act as condensers. Furthermore, since the quantity of air supplied to the interior heat exchanger is reduced, the radiated heat quantity at the interior heat exchanger is reduced, and consequently the radiated heat at the exterior heat exchanger is increased correspondingly, with the result that the ice is melted, while the passenger compartment is further heated by the interior heat exchanger, albeit with a reduced maximum power.
JP-A-5-77636 discloses a heating/cooling circuit for an air-conditioning system with an interior heat exchanger which serves as a condenser and with an exterior heat exchanger which serves as an evaporator in a heating mode, in order to heat the passenger compartment. In a defrosting mode for the exterior heat exchanger, part of the refrigerant is transferred directly from a compressor to the exterior heat exchanger as a result of the opening of a bypass, in order thereby to bypass the interior heat exchanger and an expansion valve. In this way, the exterior heat exchanger acts as a condenser and the ice is melted by the condensation heat in the exterior heat exchanger. The heat capacity of the interior heat exchanger is thereby reduced.
In both of the Japanese publications mentioned above, the heat capacity of the interior heat exchanger is reduced, even though a reduction in the temperature in the passenger interior is minimized. In the case of a continuous operation of the air-conditioning system, the defrosting mode has only a slight influence, but, in an air-conditioning system of a motor vehicle which is operated, for example, for only one hour, a defrosting mode of, for example, 30 minutes has some effect, so that there is a certain reduction in temperature in the passenger compartment.
According to a heating/cooling circuit, disclosed in EP 0 788 910 A2, for an air-conditioning system in a motor vehicle, a delay mode is described, in which the deposition of ice on the exterior heat exchanger is delayed, with the result that the heating duration can be prolonged and a defrosting mode postponed.
Air-conditioning systems of this type still do not satisfy some requirements, particularly with regard to the duration of the defrosting mode.